1. Field of the Invention
The present invention concerns a light alignment detection device. One field in which such a device finds application is that of communication with a satellite. Thus one satellite may have a laser transponder emitting a beam of light which is to be picked up by a second satellite or a ground station. Alternatively the light source could be earth-based. It will be appreciated that for the purpose of this specification the term light is not limited to visible light but includes electro-magnetic radiation extending on either side of the visible spectrum.
2. Description of Related Art
It is frequently extremely important that the emitted beam of light is accurately aligned with the optical axis of the receiving device. It is already known to use light alignment detection devices comprising a telescope associated with a detector system which captures the light beam provided it lies within a particular field aperture, the detector then providing output signals indicating the degree of misalignment of the captured beam. These signals can then be used either to alter the attitude of the emitting satellite or of the detecting device to ensure correct beam alignment. Detection devices used for this purpose have included large area coupled charge devices, CCD detectors, large area quadrant PIN diodes or small area PIN ar APD detectors in combination with mechanical scanning. All these known devices are relatively complex and bulky.